Doping through diffusion and epitaxy profile shaping

ABSTRACT

A method includes etching a semiconductor substrate to form a first trench and a second trench. A remaining portion of the semiconductor substrate is left between the first trench and the second trench as a semiconductor region. A doped dielectric layer is formed on sidewalls of the semiconductor region and over a top surface of the semiconductor region. The doped dielectric layer includes a dopant. The first trench and the second trench are filled with a dielectric material. An anneal is then performed, and a p-type dopant or an n-type dopant in the doped dielectric layer is diffused into the semiconductor region to form a diffused semiconductor region.

PRIORITY CLAIM AND CROSS-REFERENCE

This application claims the benefit of the following provisionally filedU.S. Patent Application Ser. No. 62/368,545, filed Jul. 29, 2016, andentitled “Doping Through Diffusion and Epitaxy Shaping;” whichapplication is hereby incorporated herein by reference.

BACKGROUND

Technological advances in Integrated Circuit (IC) materials and designhave produced generations of ICs, with each generation having smallerand more complex circuits than the previous generations. In the courseof IC evolution, functional density (for example, the number ofinterconnected devices per chip area) has generally increased whilegeometry sizes have decreased. This scaling down process providesbenefits by increasing production efficiency and lowering associatedcosts.

Such scaling down has also increased the complexity of processing andmanufacturing ICs and, for these advances to be realized, similardevelopments in IC processing and manufacturing are needed. For example,Fin Field-Effect Transistors (FinFETs) have been introduced to replaceplanar transistors. The structures of FinFETs and methods of fabricatingFinFETs are being developed.

The formation of FinFETs typically involves forming semiconductor fins,implanting the semiconductor fins to form well regions, forming dummygate electrodes on the semiconductor fins, etching end portions of thesemiconductor fins, and performing an epitaxy to regrow source/drainregions.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIGS. 1 through 14A are cross-sectional views and perspective views ofintermediate stages in the formation of Fin Field-Effect Transistors(FinFETs) in accordance with some embodiments.

FIG. 14B illustrates a cross-sectional view of a source/drain region ofa FinFET in accordance with some embodiments.

FIGS. 15 and 16 illustrate the cross-sectional views of intermediatestages in the formation of a source/drain region of a FinFET inaccordance with some embodiments.

FIG. 17 illustrates a cross-sectional view of a FinFET in accordancewith some embodiments.

FIG. 18 illustrates a process flow for forming FinFETs in accordancewith some embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the invention. Specificexamples of components and arrangements are described below to simplifythe present disclosure. These are, of course, merely examples and arenot intended to be limiting. For example, the formation of a firstfeature over or on a second feature in the description that follows mayinclude embodiments in which the first and second features are formed indirect contact, and may also include embodiments in which additionalfeatures may be formed between the first and second features, such thatthe first and second features may not be in direct contact. In addition,the present disclosure may repeat reference numerals and/or letters inthe various examples. This repetition is for the purpose of simplicityand clarity and does not in itself dictate a relationship between thevarious embodiments and/or configurations discussed.

Further, spatially relative terms, such as “underlying,” “below,”“lower,” “overlying,” “upper” and the like, may be used herein for easeof description to describe one element or feature's relationship toanother element(s) or feature(s) as illustrated in the figures. Thespatially relative terms are intended to encompass differentorientations of the device in use or operation in addition to theorientation depicted in the figures. The apparatus may be otherwiseoriented (rotated 90 degrees or at other orientations) and the spatiallyrelative descriptors used herein may likewise be interpretedaccordingly.

Fin Field-Effect Transistors (FinFETs) and the methods of forming thesame are provided in accordance with various exemplary embodiments. Theintermediate stages of forming the FinFETs are illustrated. Thevariations of some embodiments are discussed. Throughout various viewsand illustrative embodiments, like reference numbers are used todesignate like elements.

FIGS. 1 through 14A illustrate the cross-sectional views and perspectiveviews of intermediate stages in the formation of a FinFET in accordancewith some embodiments. The steps shown in FIGS. 1 through 14A are alsoillustrated schematically in the process flow 200 shown in FIG. 18.

FIG. 1 illustrates a cross-sectional view of substrate 20, which is apart of wafer 100. Substrate 20 may be a bulk substrate or asemiconductor-on-insulator substrate. In accordance with someembodiments of the present disclosure, substrate 20 is formed of asemiconductor material selected from, and not limited to, silicongermanium, silicon carbon, germanium, and III-V compound semiconductormaterials such as GaAsP, AlInAs, AlGaAs, GalnAs, GaInP, GaInAsP, and thelike. Substrate 20 may be lightly doped with a p-type or an n-typeimpurity. Wafer 100 includes N-type Metal Oxide Semiconductor (NMOS)region 10A and P-type Metal Oxide Semiconductor (PMOS) region 10B, inwhich a NMOS transistor and a PMOS transistor, respectively, are to beformed.

Pad oxide 22 and hard mask 24 are formed over semiconductor substrate20. In accordance with some embodiments of the present disclosure, padoxide 22 is formed of silicon oxide, which may be formed by oxidizing asurface layer of semiconductor substrate 20. Hard mask 24 may be formedof silicon nitride, silicon oxynitride, silicon carbide, siliconcarbo-nitride, or the like. In accordance with some embodiments of thepresent disclosure, mask layer 24 is formed of silicon nitride, forexample, using Low-Pressure Chemical Vapor Deposition (LPCVD). Inaccordance with other embodiments of the present disclosure, mask layer24 is formed by thermal nitridation of silicon, Plasma Enhanced ChemicalVapor Deposition (PECVD), or plasma anodic nitridation.

Next, as shown in FIG. 2, hard mask 24, pad oxide 22, and substrate 20are patterned to form trenches 26, during which hard mask 24 ispatterned first, and is then used as an etching mask to pattern theunderlying pad oxide 22 and substrate 20. Accordingly, semiconductorstrips 128A and 128B are formed in NMOS region 10A and PMOS region 10B,respectively. The respective step is illustrated as step 202 in theprocess flow shown in FIG. 18. Trenches 26 extend into semiconductorsubstrate 20, and separate semiconductor strips 128A and 128B from eachother. In the top view of wafer 100, each or some of semiconductorstrips 128A and 128B may be encircled by respective trenches 26. Inaccordance with some embodiments of the present disclosure, depth D1 oftrenches 26 is in the range between about 100 nm and about 150 nm. It isappreciated that the values recited throughout the description areexamples, and different values may also be adopted without changing theprinciple of the present disclosure.

In accordance with some embodiments of the present disclosure,semiconductor strips 128A and 128B are referred to as crown-shapesemiconductor strips. Semiconductor strip 128A includes semiconductorbase 130A and semiconductor strips 132A over base 130A. Semiconductorstrip 128B includes semiconductor base 130B and semiconductor strips132B over base 130B. Although FIG. 2 illustrates that there are threesemiconductor strips 132A (or 132B) over base 130A (or 130B), the numberof semiconductor strips 132A and 132B on each of the respective bases130A and 130B may be any integer number such as 1, 2, 3, 4, 5, or more,depending on the desirable drive currents of the resulting FinFETs. Thetop surface 130A′ of base 130A and top surface 130B′ of base 130B may besubstantially planar, or may be curved with dishing. Fin width W1 ofsemiconductor strips 132A and/or 132B may be in the range between about10 nm and about 20 nm, for example.

In accordance with some embodiments of the present disclosure, theformation of semiconductor strips 128A and 128B includes etchingsemiconductor substrate 20 to form strips 132A and 132B, formingsacrificial spacer layers (not shown) to cover the sidewalls ofsemiconductor strips 132A and 132B, and using the sacrificial spacerlayers and hard masks 24 in combination as an etching mask to furtheretch semiconductor substrate 20. The neighboring semiconductor strips132A are close to each other, and hence the portions of semiconductorsubstrate 20 between neighboring semiconductor fins 132A/132B are notetched down. As a result, bases 130A and 130B are formed. Thesacrificial spacer layers are then removed.

FIGS. 3 and 4 illustrate the formation and the removal of sacrificialliner oxide layer 34, which is formed on the exposed surfaces ofcrown-shape semiconductor strips 128A and 128B. Referring to FIG. 3,sacrificial liner oxide layer 34 is formed as a conformal layer, whosehorizontal portions and vertical portions have thicknesses close to eachother. In accordance with some embodiments of the present disclosure,sacrificial liner oxide layer 34 is formed by oxidizing wafer 100 in anoxygen-containing environment, for example, through Local Oxidation ofSilicon (LOCOS), wherein oxygen (O₂) may be included in the respectiveprocess gas. In accordance with other embodiments of the presentdisclosure, sacrificial liner oxide layer 34 is formed using In-SituSteam Generation (ISSG), for example, with water steam or a combined gasof hydrogen (H₂) and oxygen (O₂) used to oxidize the exposedsemiconductor substrate 20 and crown-shape semiconductor strips 128A and128B. The ISSG oxidation may be performed at an elevated temperaturehigher than room temperature.

Sacrificial liner oxide layer 34 is then removed, for example, in a wetetching or dry etching process, wherein HF solution or a combined gas ofNH₃ (ammonia) and HF₃ may be used. The resulting structure is shown inFIG. 4. As a result, the surfaces of crown-shape semiconductor strips128A and 128B are revealed again. The formation and the removal ofsacrificial liner oxide layer 34 may cause advantageous re-profile ofthe surfaces of crown-shape semiconductor strips 128A and 128B. Forexample, some undesired protrusions may be removed due to the higheroxidation rate of protrusions than smooth portions. The performance ofthe resulting FinFETs may thus benefit from the formation and theremoval of sacrificial liner oxide layer 34.

FIG. 5 illustrates the deposition of n-type doped dielectric layer 36A,which is deposited as a blanket layer. The respective step isillustrated as step 204 in the process flow shown in FIG. 18. Inaccordance with some embodiments, n-type doped dielectric layer 36Acomprises phosphorous, and may be a Phospho-Silicate-Glass (PSG) layer.N-type doped dielectric layer 36A may also be formed of an oxide such assilicon oxide, a nitride such as silicon nitride, or other dielectricmaterials. N-type doped dielectric layer 36A may be doped withphosphorous, arsenic, and/or antimony. N-type doped dielectric layer 36Amay be deposited using a conformal deposition method such as AtomicLayer Deposition (ALD), Chemical Vapor Deposition (CVD), or the like. Asa result, thickness T1 of the horizontal portions and thickness T2 ofthe vertical portions of n-type doped dielectric layer 36A are close toeach other, for example, with a difference smaller than about 20 percent(or 10 percent) of thickness T1. In accordance with some embodiments ofthe present disclosure, n-type doped dielectric layer 36A is aphosphorus-rich layer, wherein the atomic percentage of phosphorous inn-type doped dielectric layer 36A is higher than about 20 percent orhigher. Thicknesses T1 and T2 of n-type doped dielectric layer 36A maybe in the range between about 8 Å and about 12 Å. Furthermore, ratioT2/W1 may be in the range between about 10% and about 18%.

Further referring to FIG. 5, a patterned lithography mask is formed tocover PMOS region 10B, while leaving NMOS region 10A opened. Inaccordance with some embodiments of the present disclosure, thepatterned lithography mask includes a tri-layer, which includes bottomlayer (also known as an under layer) 38, middle layer 40 over bottomlayer 38, and upper layer 42 over middle layer 40. In accordance withsome embodiments of the present disclosure, bottom layer 38 and upperlayer 42 are formed of photo resists. Middle layer 40 may be formed ofan inorganic material, which may be a carbide (such as siliconoxycarbide), a nitride (such as silicon nitride), an oxynitride (such assilicon oxynitride), an oxide (such as silicon oxide), or the like.Upper layer 42 is patterned to form opening 44, through which n-typedoped dielectric layer 36A is removed.

Next, an anisotropic etching is performed using the tri-layer as anetching mask. In the etching process, the portion of middle layer 40 andbottom layer 38 directly underlying opening 44 is etched using thepatterned upper layer 42 as an etching mask, so that n-type dopeddielectric layer 36A is exposed. After bottom layer 38 is removed fromNMOS region 10A, an isotropic etch is performed to remove the exposedportions of n-type doped dielectric layer 36A from NMOS region 10A. Therespective step is illustrated as step 206 in the process flow shown inFIG. 18. The etching of layer 36A may include a wet etch and/or a dryetch. In the dry etch, process gases such as HF and Ar may be used. Inthe wet etch, etchant such as H₂SO₄ may be used. The portion of n-typedoped dielectric layer 36A in PMOS region 10B is protected, and is notremoved. The remaining portion of bottom layer 38 is then removed,resulting in the structure as shown in FIG. 6.

FIG. 7 illustrates the deposition of p-type doped dielectric layer 36B,which is deposited as a blanket layer. The respective step isillustrated as step 208 in the process flow shown in FIG. 18. P-typedoped dielectric layer 36B includes a p-type dopant such as boron and/orindium. P-type doped dielectric layer 36B may be formed of an oxide suchas silicon oxide, a nitride such as silicon nitride, or anotherdielectric material. In accordance with some embodiments of the presentdisclosure, p-type doped dielectric layer 36B is a Boro-Silicate-Glass(BSG) layer. P-type doped dielectric layer 36B may be deposited using aconformal deposition method such as ALD, CVD, or the like. As a result,thickness T3 of the horizontal portions and thickness T4 of the verticalportions of p-type doped dielectric layer 36B are close to each other,for example, with a difference smaller than about 20 percent (or 10percent) of T3. In accordance with some embodiments of the presentdisclosure, p-type doped dielectric layer 36B is a boron-rich layer,wherein the atomic percentage of boron in p-type doped dielectric layer36B is higher than about 35 percent or higher. Thicknesses T3 and T4 ofp-type doped dielectric layer 36B may be in the same range asthicknesses T1 and T2 of n-type doped dielectric layer 36A. In NMOSregion 10A, p-type doped dielectric layer 36B may be in physical contactwith the exposed surfaces of crown-shape semiconductor strip 128A. InPMOS region 10B, p-type doped dielectric layer 36B is separated from theunderlying crown-shape semiconductor strip 128B by n-type dopeddielectric layer 36A.

FIG. 7 further illustrates the formation of dielectric material 50,which fills the trenches separating semiconductor strips. The respectivestep is illustrated as step 210 in the process flow shown in FIG. 18.Dielectric material 50 may be formed of silicon oxide, silicon carbide,silicon nitride, or multi-layers thereof. The formation method ofdielectric material 50 may be selected from Flowable Chemical VaporDeposition (FCVD), spin-on coating, Chemical Vapor Deposition (CVD),Atomic Layer Deposition (ALD), High-Density Plasma Chemical VaporDeposition (HDPCVD), LPCVD, and the like. Dielectric material 50 may befree from n-type and p-type dopants.

In accordance with some embodiments in which FCVD is used, asilicon-containing precursor (for example, trisilylamine (TSA) ordisilylamine (DSA)) is used, and the resulting dielectric material 50 isflowable (jelly-like). In accordance with alternative embodiments of thepresent disclosure, the flowable dielectric material 50 is formed usingan alkylamino silane based precursor. During the deposition, plasma isturned on to activate the gaseous precursors for forming the flowableoxide.

After dielectric material 50 is formed, an anneal step is performed onwafer 100. The respective step is illustrated as step 212 in the processflow shown in FIG. 18. Dielectric material 50, if being flowable at thistime, will be converted into a solid dielectric material. The annealalso improves the quality of dielectric material 50, for example,resulting in the increase in the density of dielectric material 50. Inaccordance with some embodiments of the present disclosure, the annealis performed using a method selected from furnace anneal, chamberanneal, tube anneal or the like. For example, when furnace anneal isperformed, the annealing temperature may be between about 750° C. andabout 1,050° C., and the anneal duration may be in the range betweenabout 10 minutes and about 30 minutes. The annealing may be performed inan oxygen-containing environment or in an environment not containingoxygen (O₂, O₃, or the like).

In NMOS region 10A, the anneal results in the diffusion of the p-typedopant such as boron into the surface layer of crown-shape semiconductorstrip 128A. Accordingly, p-type region 52A is formed, as shown in FIG.8. The annealing causes the p-type dopant to diffuse deeper than a halfof the width W1 of semiconductor strips 132A. Accordingly, an entiretyof semiconductor strips 132A and the surface layers of semiconductorbase 130A are diffused to form p-type diffused region 52A. In PMOSregion 10B, the anneal results in both the n-type dopant in layer 36Aand p-type dopant in layer 36B to be diffused to form diffused region52B, as also shown in FIG. 8. However, since layer 36B is over layer36A, and is farther away from crown-shape semiconductor strip 128B, then-type dopant concentration is higher than the p-type dopantconcentration, and the diffused region 52B is an n-type region.Furthermore, the n-type dopant concentration in layer 36A may beadjusted to be higher than the p-type dopant concentration in layer 36Bto ensure diffused region 52B is of n-type. Similarly, the annealingcauses the n-type dopant to diffuse deeper than W1/2. Accordingly, anentirety of semiconductor strips 132B and the surface layers ofsemiconductor base 130B are n-type regions. In accordance with someembodiments of the present disclosure, the diffusion depth D2 is in therange between about 5 nm and about 20 nm.

In accordance with alternative embodiments of the present disclosure,rather than forming n-type doped dielectric layer 36A and removing itfrom region 10A, and then blanket forming p-type doped dielectric layer36B, p-type doped dielectric layer 36B is blanket formed and removedfrom region 10A, followed by forming n-type doped dielectric layer 36Aas a blanket layer. The resulting diffused regions 52A and 52B are alsoof p-type and n-type, respectively.

A planarization such as a Chemical Mechanical Polish (CMP) is thenperformed, as also shown in FIG. 9. The respective step is illustratedas step 214 in the process flow shown in FIG. 18. The remaining portionsof layers 36A and 36B and dielectric material form isolation regions 54,which are also referred to as Shallow Trench Isolation (STI) regions.Mask layer 24 may be used as the CMP stop layer, and hence the topsurface of mask layer 24 is substantially coplanar with the top surfaceof STI regions 54. Mask layer 24 is then removed, for example, usingH₃PO₄ as an etchant.

In the subsequent process steps, n-type FinFETs and p-type FinFETs areformed, for example, in NMOS region 10A and PMOS region 10B,respectively. The subsequent drawings illustrate the formation of oneFinFET, which represents both n-type FinFETs and p-type FinFETs. Forexample, referring to FIG. 10, when the respective FinFET that is to beformed is an n-type FinFET, the structure shown in FIG. 10 representsthe structure shown in NMOS region 10A (FIG. 9). Accordingly, diffusedregion 52 represents diffused p-type region 52A, strips 132 representsemiconductor strip 132A, and doped layer 36 represents p-type dopeddielectric layer 36B. Also, crown-shape semiconductor strip 128represents semiconductor strip 128A. When the respective FinFET that isto be formed is a p-type FinFET, the structure shown in FIG. 10represents the structure shown in PMOS region 10B (FIG. 9). Accordingly,region 52 represents diffused n-type region 52B, strips 132 representsemiconductor strip 132B, and doped layer 36 represents n-type dopeddielectric layer 36A and p-type doped dielectric layer 36B over layer36A. Also, crown-shape semiconductor strip 128 represents semiconductorstrip 128B. It is appreciated that both the n-type and p-type FinFETsare formed on the same wafer 100 and in the same chips.

Referring to FIG. 10, STI regions 54 are recessed, and pad layer 22(FIG. 9) may also be removed in the same process. The respective step isillustrated as step 216 in the process flow shown in FIG. 18. Therecessing of STI regions 54 may be performed using an isotropic etchingprocess, which may be a dry etch process or a wet etch process. Therecessing of STI regions 54 results in the top portions of semiconductorstrips 132 to protrude over the top surfaces of STI regions 54. Theprotruding portions are referred to as semiconductor fins (or protrudingfins) 56 hereinafter.

FIG. 11 illustrates the perspective view of the formation of dummy gatestack 58 in accordance with some embodiments of the present disclosure.The respective step is illustrated as step 218 in the process flow shownin FIG. 18. Dummy gate stack 58 may include dummy gate dielectric 60 anddummy gate electrode 62 over dummy gate dielectric 60. Dummy gatedielectric 60 may be formed of silicon oxide. Dummy gate electrode 62may be formed of polysilicon in accordance with some embodiments. Hardmasks 63, which may be formed of silicon nitride, for example, may beformed over dummy gate electrode 62.

Spacer layer 64 is formed as a blanket layer. In accordance with someembodiments of the present disclosure, spacer layer 64 is formed using aconformal deposition method such as ALD, CVD, etc., so that the sidewallportions of spacer layer 64 have an adequate thickness. The horizontalportions and vertical portions of spacer layer 64 may have substantiallythe same thickness, for example, with the vertical thickness of thevertical portions and the horizontal thickness of the horizontalportions having a difference smaller than 20 percent of the horizontalthickness.

The material of spacer layer 64 may include silicon nitride, siliconoxy-carbo-nitride (SiOCN), silicon carbo-nitride (SiOC), or a metaloxide such as aluminum oxide. In accordance with some embodiments of thepresent disclosure, spacer layer 64 is formed of SiOCN, and may have asingle-layer structure. In accordance with alternative embodiments,spacer layer 64 has a composite structure including a plurality oflayers. For example, spacer layer 64 may include a silicon oxide layer,and a silicon nitride layer over the silicon oxide layer.

Referring to FIG. 12A, an anisotropic etching is performed to remove thehorizontal portions of spacer layer 64. The remaining vertical portionsof spacer layer 64 form gate spacers 66 on the sidewalls of dummy gatestack 58, and fin spacers 68 on the sidewalls of semiconductor fins 56.The respective step is illustrated as step 220 in the process flow shownin FIG. 18. FIG. 12B illustrate a cross-sectional view of a portion ofthe structure shown in FIG. 12A, wherein the cross-sectional view isobtained from the vertical plane crossing line 12B-12B in FIG. 12A. Thecross-sectional view shown in subsequent FIGS. 13 through 16 are alsoobtained from the same vertical plane (which passes through an uncoveredportion of semiconductor fin(s) 56) crossing line 12B-12B as shown inFIG. 12A.

Next, as shown in FIG. 13, the exposed portions of semiconductor fins 56are recessed in an etching process. The respective step is illustratedas step 222 in the process flow shown in FIG. 18. In the same process,fin spacers 68 are also etched back, and the heights of the fin spacers68 are reduced. The process conditions (such as the etching selectivitybetween the etching rate of semiconductor fins 56 and the etching rateof fin spacers 68) may be adjusted so that fin spacers 68 are lowered,and some remaining fin spacers 68 are left. After the recessing ofsemiconductor fins 56 is ended, there are also some residue portions ofsemiconductor fins 56 (or semiconductor strips 132) left, and some STIportions 54 remain directly over semiconductor base 130. After theetching, the portions of semiconductor fins 56 directly underling dummygate stack 62 (FIG. 12A) remain. By adjusting the etching conditionssuch as the etchant, the temperature, the etching duration, and thematerial of fin spacers 56, the top surfaces of remaining fins 56 may beat various locations as represented by dashed lines 70.

Referring to FIGS. 14A and 14B, an epitaxy is performed to re-growepitaxy region 72, which is grown from remaining fins 56 or strip 132,but not from fin spacers 68 and STI regions 54. The respective step isillustrated as step 224 in the process flow shown in FIG. 18. Epitaxyregion 72 forms the source/drain region of the resulting FinFET. Epitaxyregion 72 may include silicon germanium doped with boron when therespective FinFET is a p-type FinFET, or may include silicon phosphorousor silicon carbon phosphorous when the respective FinFET is an n-typeFinFET.

FIG. 14A illustrates the profile of epitaxy region 72 when epitaxyregion 72 is of p-type, and the resulting FinFET is a p-type FinFET. Thecorresponding epitaxy region 72 is thus a p-type region, and diffusedregion 52 and fins 56 are n-type regions. The doping of regions 52/56advantageously results in the increase in their dopant concentrations,and the reduction of their resistance values. This advantageouslyimpacts the profile of epitaxy region 72. For example, holes 74 areformed between fins 56, and the cross-sectional views have rounded shapeand/or ellipse shape in the cross-sectional view. Angle A1 may be in therange between about 60 degrees and about 100 degrees. The height H2 ofholes 74 may be greater than the respective width W2.

FIG. 14B illustrates the profile of epitaxy region 72 when epitaxyregion 72 is of n-type, and the resulting FinFET is an n-type FinFET.The corresponding epitaxy region 72 is thus an n-type region, anddiffused region 52 and fins 56 are p-type regions. The doping of regions52/56 advantageously results in the increase in their dopantconcentrations, and the reduction of their resistance values. Thisadvantageously impacts the profile of epitaxy region 72. For example,holes 74 are formed between fins 56, and the cross-sectional views ofholes 74 include a rounded bottom portion and a triangular top portion.The triangular top portion has substantially straight edges asillustrated. Angle A2 may be in the range between about 60 degrees andabout 100 degrees. Angle A3 may be in the range between about 130degrees and about 160 degrees. In FIGS. 14A and 14B, semiconductor fins56, which still remain directly under dummy gate stack 58 (FIG. 12A),are illustrated using dashed lines since they are not in the illustrateplane.

The structures shown in FIGS. 14A and 14B may be formed on the samesemiconductor substrate 20 and in the same semiconductor chip to improvethe performance of both p-type FinFETs and n-type FinFETs. It was foundthat when the profiles as shown in FIGS. 14A and 14B are generated forp-type FinFETs and n-type FinFETs, respectively, the FinFETs have goodperformance.

FIG. 15 illustrates a cross-sectional view of the structure aftersemiconductor fins 56 as shown in FIGS. 12A and 12B are recessed/etchedin accordance with alternative embodiments. The initial steps inaccordance with these embodiments are similar to the steps shown inFIGS. 1 through 12A and 12B, and are not repeated. The processconditions for etching semiconductor fins 56 (FIGS. 12A and 12B) areadjusted, so that fin spacers 68 (FIG. 12B), semiconductor fins 56 andthe underlying semiconductor strips 132, and the portions of STI regions54 higher than semiconductor base 130 are removed. Accordingly, alldielectric materials over base 130 and in the illustratedcross-sectional view are removed. Semiconductor base 130 may beun-etched or may be slightly etched. Diffused region 52 in the topportion of base 130 still remains.

Next, as shown in FIG. 16, epitaxy region 72 is formed as a bulk region,wherein no hole is formed in epitaxy region 72. Epitaxy region 72 formsthe source/drain region of the resulting FinFET. In FIG. 16,semiconductor fins 56, which still remain directly under dummy gatestack 58 (FIG. 12A), are illustrated using dashed lines since they arenot in the illustrate plane.

Subsequently, a plurality of process steps is performed to finish theformation of the FinFET. An exemplary FinFET 80 is illustrated in FIG.17. The dummy gate stack 58 as shown in FIG. 12A is replaced withreplacement gate 78. The respective step is illustrated as step 226 inthe process flow shown in FIG. 18. Replacement gate 78 includes gatedielectric 76 on the top surfaces and sidewalls of the respective fin56, and gate electrode 77 over gate dielectric 76. Gate dielectric 76may be formed through thermal oxidation, and hence may include thermalsilicon oxide. The formation of gate dielectric 76 may also include oneor a plurality of deposition steps, and the resulting gate dielectric 76may include a high-k dielectric material or a non-high-k dielectricmaterial. Gate electrode 77 is then formed on gate dielectric 76, andmay be formed of metal layers. The formation processes of thesecomponents are not discussed in detail. Source/drain silicide regions 86are formed on the surfaces of source/drain regions 72. Source/draincontact plugs 88 are formed in Inter-Layer Dielectric (ILD) 82, and areelectrically connected to the respective source/drain silicide regions86. Diffused region 52 forms a portion of the well region for FinFET 80.

The embodiments of the present disclosure have some advantageousfeatures. By doping semiconductor strips in early stages and byadjusting the recessing of semiconductor fins during the formation ofsource/drain regions, desirable profiles may be formed for epitaxysource/drain regions, which lead to improved performance. Also, byetching a plurality of semiconductor fins and growing a bulksource/drain region, the source/drain resistance is reduced, and theperformance of the FinFETs is improved.

In accordance with some embodiments of the present disclosure, a methodincludes etching a semiconductor substrate to form a first trench and asecond trench. A remaining portion of the semiconductor substrate isleft between the first trench and the second trench as a semiconductorregion. A doped dielectric layer is formed on sidewalls of thesemiconductor region and over a top surface of the semiconductor region.The doped dielectric layer includes a dopant. The first trench and thesecond trench are filled with a dielectric material. An anneal is thenperformed, and a p-type dopant or an n-type dopant in the dopeddielectric layer is diffused into the semiconductor region to form adiffused semiconductor region.

In accordance with some embodiments of the present disclosure, a methodincludes etching a semiconductor substrate to form a semiconductorregion, which includes a semiconductor base and a plurality ofsemiconductor strips over and connecting to the semiconductor base. Afirst trench and a second trench extend into the semiconductorsubstrate, and are on opposite sides of the semiconductor region. Thefirst trench and the second trench are filled with a dielectric materialto form isolation regions. The method further includes recessing theisolation regions so that top portions of the plurality of semiconductorstrips form a plurality of semiconductor fins, forming a gate stack onfirst portions of the plurality of semiconductor fins, etching secondportions of the plurality of semiconductor fins not covered by the gatestack, and performing an epitaxy from a remaining portion of thesemiconductor region to form an epitaxy source/drain region.

In accordance with some embodiments of the present disclosure, a methodincludes etching a semiconductor substrate to form a first semiconductorregion and a second semiconductor region separated from each other bytrenches, and forming a first doped dielectric layer doped with a firstdopant having a first conductivity type. The first doped dielectriclayer is formed on sidewalls and top surfaces of the first semiconductorregion and the second semiconductor region. The method further includesremoving portions of the first doped dielectric layer on the firstsemiconductor region and forming a second doped dielectric layer dopedwith a second dopant having a second conductivity type opposite to thefirst conductivity type. The second doped dielectric layer is formed onsidewalls and top surfaces of the first semiconductor region, and coversremaining portions of the first doped dielectric layer on the secondsemiconductor region. The method further includes filling a dielectricmaterial into the trenches and over the first doped dielectric layer andthe second doped dielectric layer, and performing an anneal. The annealcauses the second dopant to be diffused into a first surface layer ofthe first semiconductor region, and the first dopant to be diffused intoa second surface layer of the second semiconductor region.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A method comprising: etching a semiconductorsubstrate to form a first trench and a second trench, wherein aremaining portion of the semiconductor substrate is left between thefirst trench and the second trench as a semiconductor region; depositinga doped dielectric layer on sidewalls of the semiconductor region andover a top surface of the semiconductor region, wherein the dopeddielectric layer is in physical contact with a semiconductor material ofthe semiconductor region, and wherein the doped dielectric layercomprises a dopant; forming a first dielectric region and a seconddielectric region in the first trench and the second trench,respectively, wherein the first dielectric region and the seconddielectric region overlap bottom portions of the doped dielectric layer;performing an anneal, wherein the dopant in the doped dielectric layeris diffused into the semiconductor region to form a diffusedsemiconductor region; and forming a gate stack comprising a gatedielectric and a gate electrode over the gate dielectric, wherein thegate dielectric is in physical contact with the diffused semiconductorregion.
 2. The method of claim 1, wherein the semiconductor regioncomprises a semiconductor base, and semiconductor strips over andconnecting to the semiconductor base, and the method further comprises:etching the semiconductor strips; and performing an epitaxy from aremaining portion of the semiconductor region to form an epitaxysemiconductor region.
 3. The method of claim 2 further comprising:forming gate spacers on sidewalls of the gate stack; forming fin spacerson sidewalls of top portions of the semiconductor strips; and recessingthe top portions of the semiconductor strips between the fin spacers,wherein portions of the epitaxy semiconductor region grown fromremaining portions of the semiconductor strips merge with each other. 4.The method of claim 2, wherein the epitaxy is grown from the diffusedsemiconductor region.
 5. The method of claim 1, wherein the dopant inthe doped dielectric layer is of n-type, and the method furthercomprising forming an additional p-type doped layer, wherein a portionof the additional p-type doped layer overlaps the doped dielectric layerbefore the anneal.
 6. The method of claim 1, wherein the forming thedoped dielectric layer comprises depositing a Phospho-Silicate-Glass(PSG) layer.
 7. The method of claim 1, wherein the forming the dopeddielectric layer comprises depositing a Boro-Silicate-Glass (BSG) layer.8. A method comprising: etching a semiconductor substrate to form asemiconductor region comprising a semiconductor base and a plurality ofsemiconductor strips over and connecting to the semiconductor base,wherein a first trench and a second trench extending into thesemiconductor substrate are on opposite sides of the semiconductorregion; forming a first doped dielectric layer contacting sidewalls ofthe semiconductor region, wherein the first doped dielectric layercomprises a portion having a bottom surface contacting a top surface ofa bulk portion of the semiconductor substrate, wherein the bulk portionis directly underlying the first trench, and the first doped dielectriclayer comprises a first dopant of a first conductivity type; forming asecond doped dielectric layer doped with a second dopant having a secondconductivity type opposite to the first conductivity type, wherein thesecond doped dielectric layer overlaps the first doped dielectric layer;performing an annealing process to diffuse dopants in both of the firstdoped dielectric layer and the second doped dielectric layer into eachof the plurality of semiconductor strips; filling the first trench andthe second trench with a dielectric material to form isolation regions;recessing the isolation regions, wherein top portions of the pluralityof semiconductor strips form a plurality of semiconductor fins; forminga gate stack on first portions of the plurality of semiconductor fins;etching second portions of the plurality of semiconductor fins notcovered by the gate stack; and performing an epitaxy from a remainingportion of the semiconductor region to form an epitaxy source/drainregion.
 9. The method of claim 8 further comprising: forming fin spacerson sidewalls of the second portions of the plurality of semiconductorfins; and recessing the fin spacers when the plurality of semiconductorfins is etched.
 10. The method of claim 9, wherein when the epitaxy isstarted, the fin spacers have portions remaining, and the remainingportions of the fin spacers are opposite sides of the epitaxysource/drain region after the epitaxy source/drain region is formed, andthe remaining portions of the fin spacers are in contact with portionsof the plurality of semiconductor fins that are doped with the firstdopant and the second dopant to form vertical interfaces.
 11. The methodof claim 8, wherein during the annealing process, the second dopeddielectric layer is in physical contact with the first doped dielectriclayer.
 12. The method of claim 8 further comprising forming a firstdielectric region and a second dielectric region in the first trench andthe second trench, respectively, wherein the first dielectric region andthe second dielectric region overlap, and are in contact with, bottomportions of the second doped dielectric layer.
 13. The method of claim8, wherein the first doped dielectric layer contacts sidewalls of thesemiconductor base to form a vertical interface.
 14. A methodcomprising: etching a semiconductor substrate to form a firstsemiconductor region and a second semiconductor region separated fromeach other by trenches; forming a first doped dielectric layer dopedwith a first dopant having a first conductivity type, wherein the firstdoped dielectric layer is formed on sidewalls and top surfaces of thefirst semiconductor region and the second semiconductor region; removingportions of the first doped dielectric layer on the first semiconductorregion; forming a second doped dielectric layer doped with a seconddopant having a second conductivity type opposite to the firstconductivity type, wherein the second doped dielectric layer is formedon sidewalls and top surfaces of the first semiconductor region, andcovers remaining portions of the first doped dielectric layer on thesecond semiconductor region; filling a dielectric material into thetrenches and over the first doped dielectric layer and the second dopeddielectric layer; and performing an anneal, wherein the second dopant isdiffused into a first surface layer of the first semiconductor region,and the first dopant is diffused into a second surface layer of thesecond semiconductor region.
 15. The method of claim 14, wherein thefirst surface layer of the first semiconductor region is of the secondconductivity type, and the second surface layer of the secondsemiconductor region is of the first conductivity type.
 16. The methodof claim 15, wherein the second dopant is also diffused into the secondsurface layer of the second semiconductor region during the anneal. 17.The method of claim 14, wherein the forming the first doped dielectriclayer comprises depositing a Phospho-Silicate-Glass (PSG) layer.
 18. Themethod of claim 14, wherein the forming the second doped dielectriclayer comprises depositing a boro-Silicate-Glass (BSG) layer.
 19. Themethod of claim 14 further comprises: removing portions of the firstsemiconductor region; and performing an epitaxy to grow an epitaxyregion from the first surface layer.
 20. The method of claim 1, whereinthe first dielectric region and the second dielectric region are formedafter the anneal.